Domain propagation arrangement

ABSTRACT

Single wall domains are moved in a slice of magnetic material by magnetically soft overlay patterns on both surfaces of the slice. The overlays are shaped alike and are offset one from the other along the axis of domain movement so that each provides pole patterns to attract a domain to the same consecutive positions as a magnetic field reorients in the plane of the slice.

United States Patent [72] Inventors PeterlJonyhard Newark; Donald E. Klan, North Plalntleld; James L. Smith, Bedmhater all of, NJ.

[2|] AppLNo. 866,869

[22] Filed Oct. 16,1969 v [45] Patented Aug-3,1971

[73] Asaignee Bell'l'elephoneLaboratorles Incorporated Murray Hill, NJ.

[54] DOMAIN PROPAGATION MGM 5 ClnhaJDrawlng I;

[52] US.- 40/1748, 340N741? [5|] IIL Gllell/ld, on Io 19/00 1501 mam 340/174 TF, 174 SR m lelerencesCited uurren s'umas PATENTS 3,534,341 10/1910 Bobeck 340/174 Primuy Examiner-James W. Moffitt Anomeyr- R. J. Guenther and Kenneth B. Hamlin AIS'IIACT: Single wall domains are moved in a slice of magnetic material by magnetically sofi overlay patterns on both surfaces of the slice. The overlays are shaped alike and are offaet one from the other along the axis of domain movement so that each provides pole patterns to attract a domain to the ante consecutive positions as a magnetic field reorients in the plane of the slice.

DOMAIN PROPAGATION ARRANGEMENT FIELD OF THE INVENTION propagation devices.

BACKGROUND OF THE INVENTION Domain propagation devices are well known in the. art. In

most known domain propagation devices, a reverse-magnetized domain, having spaced apart leading and trailing domain walls, is moved controllably in a channel structured to prevent lateral motion of the domain. The Bell System Technical Journal (BSTJ), Volume XLVI, No 8,0ct. l967,at page l90let seq., on the other hand, describes a domain which is (self) bounded by a single domain wall andis free to move in the plane of the sheet. Movement of a domain in the'latter case is in response to an offset structured magnetic field (gradient) which displaces the domain in the absence of uncontrolled expansion thereof.

A typical magnetic sheet in which single wall domains are moved comprises, for example, a rare earth orthoferrite or a strontium or barium ferrite. The domains assume the shape of right circular cylinders, the axes of which are normal to the plane of a sheet of these materials. The sheets are characterized by a preferred direction of magnetization normal to the sheet, magnetization in a first direction along that normal being considered negative and magnetization in a second direction being considered positive A convenient convention is to represent a single wall domain in such a sheet as an encircled plus sign where the circle in the plane of the sheet represents the encompassing single wall of the domain. In connection with the ensuing discussion, the plus sign'may be omitted and the domain represented solely as a circle, it being implicitly understood that the magnetization elsewhere in the sheet other than within circles is negative.

There are a variety of techniques for moving'single wall domains. One comprises offset conductor loops pulsed in sequence to displace domains to next consecutive positions.

The displacement is effected by the magnetic field gradient temporarily induced by the current pulse in the conductors.

This technique permits highly flexible control over individualcal domain, for example, domains of the order of microns in diameter.

Another technique for moving single wall domains employs a magnetically soft structured overlay on the sheet in which single wall domains are moved. Such an arrangement is disclosed in copending application Ser. No. 732,705,filed May 28, l968and now U.S. Pat. No. 3,534,347for A. H. Bobeck. The overlay generates a dynamic pattern of magnetic poles which move in the overlay in response to controlled changes in direction of an externally produced magnetic field applied parallel to the plane of the sheet. The poles attract or repel domains along a predictable path detennined by the particular overlay pattern and consecutive orientations of the externally applied magnetic field.

The latter technique has the virtue that the structured overlay that physically establishes the position and the motion of the domains is not required to carry currents and so can be substantially thinner than current-carrying conductors; The fine line overlay pattern consequently, offer fewer technologi= cal difficulties when manufactured in the dimensions'required to manipulate domains of minute size. The technique also permits the movement of all domains'in a sheet without discrete wiring connections.

A propagation technique employing such an overlay is clearly attractive for recirculating type memories, such as disc files, where information ismoved constantly and the read and write operations are carried out at a common location. This type of organization is presently realized in accordance with prior art electromechanical techniques which provide economy and reliability'by' reducing the number of detection and input circuits. No external connections are required except at the common write-read location.

An object of this invention is to provide a domain propagation device including a magnetically sofl overlay geometry which offers reduced power requirements for moving single wall domains in ama'gnetic material responsive to reorienting in-plane fields.

BRIEF DESCRIPTION OF THE INVENTION Propagation techniques employing overlays and responsive to reorienting in-plane fields are improved in accordance with this invention by including two overlay patterns on opposite surfaces of the material in which single wall domains are moved. Illustratively, each'overlay is configured essentially identically. The materials in which single wall domains are moved typically are characterized by a magnetization normal to the plane of the material. A single wall domain in such a material can be considered magnetically negative at one surface and'magnetically positive at another. A single overlay configuration on one surface can function to move domains. The same overlay on the opposite surface also functions independently to move the'domains. If only one overlay were present at a'time, in the latter instance, a domain would be one-half cycle of the in-plane field behind the position of the domain'in'the former instance. By employing two overlays of like configuration, one being offset one-half cycle with respect to the other, the two configurations function in concert in response to the reorienting in-plane field to advance domain patterns to the same consecutive positions in the material therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION FIG. 1 shows an arrangement 10 including a sheet or slice 11 of material in which single wall domains can be moved. An overlay pattern 12 of magnetically soft material defines a propagation channel in slice 11 between input and output positions I and 0 respectively in response to, illustratively, a rotating in-plane field. Typically, the overlays are photodeposited on glass and juxtaposed with the surfaces of slice llQAn in-plane field source is represented in FIG. 1 by a block 13.

An illustrative input portion of the arrangement of FIG. 1 comprises a magnetically soft disc 14 to the periphery of which a domain D is coupled. As the in-plane field reorients, domain D moves about 14 giving rise to a domain for propagation when the magnitude of the in-plane field is augmented appropriately. Such an input arrangement is disclosed in copending application Ser. No. 756,2l0,filed Aug. 29, l968for A. .l. Pemeski. The provision 'of augmented in-plane fields is represented generally by line 16 in FIG. 1.

Magnetic polesmove in the illustrative overlay pattern to attract domain patterns to the right as viewed in response to an in-plane field rotating clockwise. When a domain so moved reaches the output position its flux is detected by a conductor loop indicated at'l8 for detection by a utilization circuit 19 to which it is connected. In practice an additional conductor looptnot shown) may be present to collapse any domain at the position coupled by loop 18 when pulsed.

Source 13 and circuit 19 are connected to a control circuit 20 for synchronization and activation. Such circuits and sources may be any such elements capable of operating in accordance'with this invention.

The operation of a single overlay to move domains as required is fully disclosed in the above-mentioned application of Bobeck and is not described in detail herein.

It is quite clear that a single overlay can be disposed as shown in FIG. 1 on either surface of slice 11. Consider the condition where an overlay pattern is disposed on each side of slice 11 between the input and output position. For example, FIG. 2 shows a domain D1 of FIG. 1 in a portion of slicel l.

The domain is assumed to be magnetically positive on the top surface of slice 11 as viewed and negative on the bottom surface. This condition is represented by the plus and minus signs in slice 11 in FIG. 2. When the in-plane field is in an orientation as represented by arrow H, poles form at the ends of overlay segments aligned with the field, plus poles at the ends associated with the tip of arrow H, minus poles at the other end. For the geometry shown, each of the poles so generated on the pertinent portions of the overlays HT and 12B are such as to attract the domain. in the absence of one of the overlays, the poles so generated are operative only on one surface of the sheet.

- The top and bottom overlays are, illustratively, 180 out-ofphase with respect to one another along an axis between the input and output position because the overlay configuration on one surface is disposed to generate negative poles at the same time the overlay on the opposite surface is generating positive poles in response to the same in-plane field orientation. The phase relation in this connection finds its origin in the consecutive orientations of the in-plane field. The orientation shown by arrow H in FIG. 2 is taken as a first phase. A reversed arrow would be in a third phase. The overlays at any particular position are of a geometry such that they respond to generate opposite poles at that position in response to a given in-plane field. This relationship is described herein as 180 out-of-phase.

Not only does a field of a given magnitude produce double the pole attraction of a single overlay configuration by generating double the number of poles but a closed magnetic structure is also produced. This is clear from FIG. 3 which shows a cross section of overlays l2 and 12' of FIG. 1 along an axis between the input and output positions. When the inplane field is oriented as indicated by arrow H in H6. 3, poles of polarities indicated are generated in the overlay and flux closes as indicated by the arrows within the representation of slice 11. When the field is oriented as shown in FIG. 2, flux closure of a similar type is pennitted through the overlays defining parallel channels as indicated in FIG. 1. It is contemplated that large numbers of parallel channels will be defined within any practical embodiment.

Complementing overlays on opposite surfaces also impose a relatively confining structure for pole patterns thus reducing any tendency of those poles to be distorted because of crystal imperfections in sheet 111. The chances of crystal imperfections deflecting domains from their channels is thus significantly reduced. Y

The advantages of offset overlays in accordance with this invention are clear from a comparison of operating parameters of a single overlay arrangement with a complementing overlay arrangement. For a slice of SmTbFeO having a thickness of about 2mils and domains having 2-mil diameters, a rotating inplane field of over 8oersteds moves a domain pattern at. a given data rate. In this instance, the overlay is permalloy having a coercive force of about loersted. The overlay is =4,000 A. thick and has a repeat of 8mils. If a double overlay pattern is used in accordance with this invention, the same data rate is achieved with an in-plane field of less than 4oersteds. A bias field normal to the plane of slice 11 is usually provided during operation. A typical field is 45oersteds.

What has been described is considered only illustrative of the principles of this invention. Therefore, a variety of modifications can be devised by those skilled in the art in accordance with those principles still within the spirit and scope of this invention.

What is claimed is: 1. Apparatus comprising a material in which single wall domains can be moved and having first and second surfaces, means comprising first and second overlays adjacent said first and second surfaces for defining a propagation channel for single wall domains between input and output positions in said material in response to a reorienting in-plane field, said overlays being of a material and having first and second geometries offset with respect to one another between said input and output positions such that each generates poles to attract domains to like consecutive positions in said channel in response to said in-plane field.

2. Apparatus in accordance with claim 1 wherein said first and second geometries are alike.

2. Apparatus in accordance with claim 2 wherein each of said overlays comprises T-shapes and bars and said in planc field reorients by rotation.

4. Apparatus in accordance with claim 3 wherein said overlay material comprises magnetically soft permalloy.

5. Apparatus in accordance with claim 4 wherein the bars and T-shapes of each overlay alternate and the bars of said first overlay are disposed opposite the T-shapes of said second overlay. 

1. Apparatus comprising a material in which single wall domains can be moved and having first and second surfaces, means comprising first and second overlays adjacent said first and second surfaces for defining a propagation channel for single wall domains between input and output positions in said material in response to a reorienting in-plane field, said overlays being of a material and having first and second geometries offset with respect to one another between said input and output positions such that each generates poles to attract domains to like consecutive positions in said channel in response to said inplane field.
 2. Apparatus in accordance with claim 2 wherein each of said overlays comprises T-shapes and bars and said in-plane field reorients by rotation.
 2. Apparatus in accordance with claim 1 wherein said first and second geometries are alike.
 4. Apparatus in accordance with claim 3 wherein said overlay material comprises magnetically soft permalloy.
 5. Apparatus in accordance with claim 4 wherein the bars and T-shapes of each overlay alternate and the bars of said first overlay are disposed opposite the T-shapes of said second overlay. 